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RESEARCH PRODUCT

Detection of the Lowest-Lying Odd-Parity Atomic Levels in Actinium

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Two lowest-energy odd-parity atomic levels of actinium, 7s27pP21/2o, 7s27pP23/2o, were observed via two-step resonant laser-ionization spectroscopy and their respective energies were measured to be 7477.36(4) and 12 276.59(2) cm-1. The lifetimes of these states were determined as 668(11) and 255(7) ns, respectively. In addition, we observed the effect of the hyperfine structure on the line for the transition to P23/2o. These properties were calculated using a hybrid approach that combines configuration interaction and coupled-cluster methods, in good agreement with the experiment. The data are of relevance for understanding the complex atomic spectra of actinides and for developing efficient laser cooling and ionization schemes for actinium, with possible applications for high-purity medical-isotope production and future fundamental physics experiments. © 2020 American Physical Society. The authors thank V. V. Flambaum and V. A. Dzuba for stimulating discussions and providing the corrected lifetimes, and M. Block, Ch. Mokry, and J. Runke for providing the actinium sample. We gratefully acknowledge discussions with R. Beerwerth and S. Fritzsche on the theory of the actinium hyperfine structure. The work was supported by the German Federal Ministry of Education and Research under the Projects No. 05P15UMCIA, No. 05P18UMCIA. D. B. was supported in part by the DFG Project ID 390831469: EXC 2118 (). D. B. also received support from the European Research Council (ERC) under the European Union Horizon 2020 Research and Innovation Program (Grant Agreement No. 695405), from the DFG Reinhart Koselleck Project. Theory work was supported in part by U.S. NSF Grant No. PHY-1620687. S. G. P. and M. G. K. acknowledge support by the Russian Science Foundation under Grant No. 19-12-00157.